In a thermal inkjet printhead, the thin film heater plays the most important role because it must fire over 1 billion times during the device operation. The temperatures are up to several hundreds degrees Celsius during firing and the duration is on the order of microsecond. The resistance stability and mechanical property of the thin film resistor are very critical for fabrication. In this study, the resistivity and stress behavior related to a wide range of tantalum-aluminum (Ta-Al) compositions by sputtering are examined. For the Al content between 12% and 60% atomic ratio, no significant change in resistivity was found. The films with small Al ratios (≤ 12%) exhibit poor thermal stability and the compressive stress increases after each thermal cycle (from 25 to 450°C), while the films with larger Al atomic ratios show good stability. The stress-temperature behavior of various Ta-Al compositions during thermal cycle will be discussed. An open pool environment is arranged such that the liquid pool can be regarded as an infinite reservoir for the heater, from the standpoint of both momentum and energy transport. Early failure due to high stress level in the thermal inkjet device is evident.